Messages in this thread |  | | | Date | Thu, 22 Dec 2005 22:39:13 +0100 | | From | Eric Dumazet <> | | Subject | Re: [PATCH RT 00/02] SLOB optimizations |
Ingo Molnar a écrit : > * Eric Dumazet <dada1@cosmosbay.com> wrote: > >>> in any case, on sane platforms (i386, x86_64) an irq-disable is >>> well-optimized in hardware, and is just as fast as a preempt_disable(). >> I'm afraid its not the case on current hardware. >> >> The irq enable/disable pair count for more than 50% the cpu time spent >> in kmem_cache_alloc()/kmem_cache_free()/kfree() > > because you are not using NMI based profiling? > >> oprofile results on a dual Opteron 246 : >> >> You can see the high profile numbers right after cli and popf(sti) >> instructions, popf being VERY expensive. > > that's just the profiling interrupt hitting them. You should not analyze > irq-safe code with a non-NMI profiling interrupt. >
I'm using oprofile on Opteron, and AFAIK it's NMI based.
# grep NMI /proc/interrupts ; sleep 1 ; grep NMI /proc/interrupts NMI: 391352095 2867983903 NMI: 391359678 2867998498
thats 7583 and 14595 NMI / second on cpu0 and cpu1 respectivly in this sample.
> CLI/STI is extremely fast. (In fact in the -rt tree i'm using them > within mutexes instead of preempt_enable()/preempt_disable(), because > they are faster and generate less register side-effect.) > > Ingo > >
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